Method of producing light hydrocarbons



Aug. 1, 1939. R. M. lSHAM 2,168,261

umnon OF raonucms LIGHT nynnocmsous Filed Dec. 14, 19:52

Patented Aug. 1, 1939 UNITED STATES METHOD OF PRODUCING LIGHTHYDROCARBONS Robert M. Isham, Okmulgee, 0kla., assignor of three-fourthsto William B. Pine, Okmulgee,

Okla.

Application December 14, 1932, Serial No. 647,281

2 Claims.

This invention relates to a method of producing light hydrocarbons, andmore particularly to the production of gasoline.

In the extraction of gasoline from casinghead gas or from natural gas,whether by compression and liquefaction or by absorption, there isobtained along with the stable gasoline a' large amount of materialwhich is highly volatile because of its high vapor tension. Heretoforemuch of this material has been wasted by evaporation into the air in thecourse of weathering, while where use has been made of this material ithas been largely used in vapor form as a fuel, or held in liquid formunder pressure and sold as liquefied petroleum gas for use in gasgenerators and the like. This highly volatile material is largelycomposed of saturated hydrocarbons or members of the paraifin series,principally propane, isobutane and butane.

While it has heretofore been proposed to subject this highly volatilematerial to pyrogenetic decomposition so as to produce unsaturatedhydrocarbons and free hydrogen, and efforts have been made to use theseunsaturated hydrocarbons, as by polymerization under the influence ofhigh temperature and pressure in the presence of a suitable catalyst, orby combining them with one or more of the hydrocarbons of the aromaticseries, as naphthalene, under suitable conditions with or without thepresence of a catalyst, so far as I am aware none of these proposedprocedures has proved entirely satisfactory, if in fact usable, for thecommercial production of gasoline.

It has also been proposed to subject casinghead or natural gas to arelatively high temperature and pressure and then introduce it into astill in conjunction with petroleum oil to be cracked, the heated gasbeing used as the sole source of heat for the cracking process so as toprevent undesirable separation of carbon in the still by overheating ofportions of the oil therein, but this heating of the saturated gaseoushydrocarbons of the paraflin series under a relatively high pressure isnot accompanied by any efficient decomposition of the saturatedhydrocarbons into unsaturated hydrocarbons.

In order to improve upon these known processes, I have heretoforeproposed, in my application Serial No. 510,839, filed January 23, 1931,to utilize the highly volatile, saturated hydrocarbons obtained in anysuitable way during the abstraction of gasoline from casinghead ornatural gas for increasing the yield of stable gasoline produced bycracking petroleum oil. In

this prior process I discovered that if the highly volatile hydrocarbonsextracted from casinghead or natural gas are subjected at substantiallyatmospheric pressure to any suitable cracking process, so as to obtain amaximum yield of unsaturated hydrocarbons, particularly olefins, and ifthese unsaturated hydrocarbons are then raised to or above a certaincritical pressure and then intermingled with petroleum oil, also at orabove the critical pressure, and at the cracking 1 temperature, theolefins will interact and react with the fractions obtained by thecracking process, producing an increased yield of gasoline.

While this last mentioned process provides a greatly improved method ofcracking petroleum 15 oil so as to obtain an increased yield of thedesired lighter hydrocarbons, and in fact yields a volume of gasolinegreater than that of the petroleum oil treated, I have since discoveredstill another method of utilizing the highly vola- 20 tile, saturatedhydrocarbons extracted from casinghead or natural gas for the productionof gasoline wherein the gasoline is produced entirely from theuncondensed hydrocarbon gases without the addition to the system of anypetroleum oil as required by my prior method.

It is therefore one of the objects of the present invention to provide anovel method of utilizing the highly volatile constituents derived fromcasinghead or natural gas for the production of a light. hydrocarbons,such as those of the naphtha class.

Another object is to provide an improved method of treating hydrocarbonswherein gasoline is produced entirely from the uncondensed, highlyvolatile, saturated hydrocarbon gases obtained during the abstraction ofgasoline from casinghead or natural gas, and without the additionthereto of any petroleum oil.

A further object is to provide a novel method of producing gasoline bypolymerization under pressure of the unsaturated hydrocarbons derivedfrom' the highly volatile, saturated hydrocarbons obtained fromcasinghead and natural gas. 45

Another object is to provide a novel method of producing gasoline bypolymerization under pressure of unsaturated hydrocarbons wherein theheavier oils resulting from the process are recycled so as to controlthe character of the 50 polymerization product.

These and other objects will appear more fully upon a consideration ofthe detailed description of the invention which follows. Although onlyone embodiment of the process and an apparatus for 55 carrying out thesame has been described and diagrammatically illustrated, it is to beexpressly understood that the description and drawing are for thepurpose of illustration only and are not to be construed as defining thescope of the invention, reference being had for this purpose to theappended claims.

In practicing the method of the present invention, although casingheadgas and natural gas may be used directly, I prefer to extract from thecasinghead or natural gas the stable gasoline and the highly volatilehydrocarbons, leaving the dry" hydrocarbon gas for use as a gas, and tothen separate the highly volatile hydrocarbons from the stable gasoline.The highly volatile hydrocarbons so obtained are then subjected atsubstantially atmospheric pressure to any suitaable cracking process soas to obtain a maximum yield of unsaturated hydrocarbons, particularlyolefins, which are obtained with hydrogen and some saturated hydrocarbongases.

I have discovered that if, after this olefin hearing gas is preferablycooled, it is compressed to or above what may be called a criticalpressure, such as 600 pounds or more per square inch, and then mixedwith hot oil from a later stage of the process, said oil also being ator above the critical pressure, and the mixture of gas and oil is heatedto the polymerization temperature of the unsaturated hydrocarbonspresent in the gas, preferably to about 775 F., the oil is largelyvaporized and dilutes the gaseous hydrocarbons during polymerization soas to prevent excessive polymerization to hydrocarbons heavier thangasoline. The heavier polymers of the oil thus displace the equilibriumpoint of polymerization so that the polymerization product consists ofgasoline hydrocarbons rather than hydrocarbons of heavier classes.

From the polymerization element such as a coil the mixture of gas, oiland oil vapors may pass to a separator where any liquid oil is removed,the gas and oil vapors then passing through a pressure reducing valve,whereby the pressure is reduced to about 100 pounds per square inch,into a dephlegmation tower in which fractionation occurs. The spent gasand gasoline vapors may then be collected and separated in any desirablemanner, while the heavy hydrocarbons which have been produced duringpolymerization are collected in the bottom of the dephlegmation tower inthe form of oil and continuously pumped therefrom back to the inlet tothe polymerizing coil where it again mingles with the compressedunsaturated hydrocarbons. The unvaporized oil collected in the separatoris also recirculated, first through a tar still in which the morevolatile portions are separated, and then through a condenser fromwhence said portions are pumped back to the polymerizing chamber througha heater exposed to the hot vapors within the dephlegmation tower.

Any suitable apparatus may be employed for carrying out the method justdescribed, and any suitable temperatures and pressures may be useddependent upon the particular conditions to be observed and results tobe obtained. As one embodiment of the invention, however, the followingprocedure may be taken as exemplary, reference being had for purposes ofillustration to the accompanying diagrammatic drawing: the uncondensed,highly volatile, saturated hydrocarbon gases from the distillation unitof a plant for extracting gasoline 'from casinghead or natural gas enterthe system through a pipe I and are first passed through heater tubes 2in a suitable furnace 3 wherein they attain a temperature of from 1300to 1350 F. at substantially atmospheric pressure and are cracked so asto yield a substantial percentage of unsaturated hydrocarbons. It hasbeen found that during this cracking step the volume of the incominggases is increased from 60% to 100%, and a cracked gas is produced whichcontains approximately 30% unsaturated hydrocarbons. The cracked gasthen passes through the cooling coil 4 of a suitable cooler 5 whereinits temperature is reduced to substantially that of the atmosphere.

The cooled, unsaturated hydrocarbon gas is then compressed, as by asuitable pump 6, to what is a critical pressure for the ensuingreaction, for example a pressure of 600 pounds per square inch or more,and conducted from the pump through a pipe I to a T connection 8 leadinginto the coil 9 of apolymerization heating chamber In. The pressure tobe employed may greatly exceed the pressure of 600 pounds per squareinch stated above, the reaction taking place more rapidly as thepressure is increased. Good results are obtained, for example, with 1000pounds pressure. Economic considerations, however, make it desirable tokeep the pressure low in order to reduce costs. the compressed,unsaturated hydrocarbons are mixed with hot oil which is suppliedthereto, also under a corresponding pressure, through a pipe II from thedephlegmation tower and tar still later to be described. The mixture ofunsaturated hydrocarbon gases and oil is then heated in its passagethrough coil 9 of polymerizing chamber H] to the polymerizationtemperature of the unsaturated hydrocarbons, this temperature preferablybeing in the neighborhood of 775 F.

,During its passage through polymerizing coil 9, a large proportion ofthe oil is vaporized and the vapors of these heavier polymers serve todilute the unsaturated gaseous hydrocarbons during polymerization and toprevent excessive polymerization to hydrocarbons heavier than gasoline.They also serve to assist in regulating the temperature within thepolymerizing coil by absorbing a portion of the heat given off by thestrongly exothermic polymerization reaction. The introduction of the oilprior to polymerization thus displaces the equilibrium point ofpolymerization and results in gasoline hydrocarbons as thepolymerization product.

From polymerization coil 9, the mixture of gas, oil and oil vaporspasses through a pipe l2 to a suitable separator 13 wherein any liquidoil may be separated out. of the separator l3 through pipe l4, and,after passing through a pressure reducing valve l5 of any suitableconstruction, wherein the pressure may be reduced to approximately 100pounds per square inch, are supplied to a dephlegmation tower I6 whereinfractionation occurs. After fractionation the spent gas and vapors offinished gasoline hydrocarbons leave the top of dephlegmation tower l6through a pipe I! and are supplied thereby to a suitable condenser I8wherein the gasoline is condensed. At the same time, any heavierhydrocarbons which have been produced by the polymerization step descendto the bottom of dephlegmation tower 16 in the form of oil, said oilbeing removed therefrom through a suitable pipe I9 by a hot oil pumpwhich raises its pressure to substantially the same critical pressure asthat produced by gas pump 6 and returns the oil through pipes 2| and Hto T 8 where it again AtTB.

The gas and oil vapors pass out mixes with the compressed cracked gasand reenters the polymerizing coil 9.

From condenser i8 the spent gas and gasoline flow to a suitableseparator 22 wherein they separate by gravity. The spent gas, which nowcontains only a fraction of 1% of unsaturated hydrocarbons, is drawn oilthrough pipe 23 and pressure reducing valve 24 and supplied therefrom tothe fuel supply. A portion of the gasoline which is removed fromseparator 22 is pumped back to dephlegmation tower l6 through a pipe 25by pump 26, the quantity pumped back being regulated so as to produce agasoline of the desired end point. The balance of the gasoline is thendrawn off through pipe 21 to storage.

Any unvaporized oil which separates out in separator I3 is drawn ofitherefrom through a pipe 28, and, after passing through a suitablepressure reducing valve 29 wherein its pressure is reduced substantiallyto atmospheric, is supplied to a tar still 30 of any suitableconstruction. In the tar still the more volatile portions of the oil arevaporized, andfrom thence they pass into a condenser 3| wherein they areagain reduced to liquid form and accumulate as liquid distillate in asuitable receiver 32. The undistilled tar which drains down to thebottom of tar still 30 is run off through a pipe 33 and valve 34 tostorage. Liquid distillate from receiver 32 is supplied therefromthrough a pipe 35 to a suitable pump 36 wherein its pressure is raisedto substantially the same pressure as that produced by pumps 6 and 20,and by which it is supplied, passing through a heating coil 31 en routewhich may be exposed to the hot vapors within the dephlegmation towerIt, to a T 38 where it joins the hot oil from the bottom 01'dephlegmation tower I6 and passes on to T 8 and reenters thepolymerizing coil 9.

The operation of the system thus described can be regulated by raisingor lowering the tempera ture within polymerizing coil 9, to decrease orincrease the production of oils heavier than gasoline, so that theamount of heavy oil pumped back is constant, and only gasoline, tar andspent or dry gas leave the system. Thus an increase in temperaturewithin polymerizing coil 9 will cause a partial depolymerization of therecycled oil, converting it partially to gasoline and decreasing theamount of heavy products returned from dephlegmation tower I6. I havefound, however, that at a temperature of approximately 775 F. the amountof polymers returning from tower l6 remains substantially constant, andthere is no accumulation of heavy oils in the system.

In practicing the method thus described, I have been able to produceapproximately eight gallons of gasoline, or naphtha, per 1,000 cubicfeet of uncondensed, saturated hydrocarbon gas treated. The gasoline, ornaphtha, produced is usually from 52 to 57 Baum gravity and is of veryhigh octane number. By blending the product of my method with asufllcient quantity of high gravity natural gasoline produced fromcasinghead or natural gas, to give a product of suitable volatility, afinished motor fuel of extremely fine quality and high octane number maybe produced.

.In starting the operation oi. the system thus described, it may eitherbe operated without addition of oil so as to produce its own charge ofoil for cycling, or a small quantity of recycled gas oil from an oilcracking unit may be placed in the system to give a suitable initialquantity of oil for cycling through the system.

It will thus be seen that by the present invention there is provided anovel method for utilizing the highly volatile, saturated hydrocarbonconstituents of the abstraction product from casinghead or natural gasso as to produce gasoline without the addition to the system of anyother material, such as petroleum oil. The gasoline is produced bypolymerization of the unsaturated hydrocarbon gases which are crackedfrom the highly volatile, saturated starting gas, and the heavier oilsresulting from the process may be recycled through the polymerizing collso as to control the character of the polymerization product and toresult in gasoline hydrocarbons of high quality. With this process, theresulting products of gasoline, spent gas and tar are obtained entirelyfrom the highly volatile, saturated hydrocarbon gases which form thesole starting material, and it is not necessary to add to the system anypetroleum oil or other similar material.

While the method has been described with considerable particularity asapplied to the production of gasoline by polymerization of unsaturatedhydrocarbons, it will be appreciated by those skilled in the art thatthe invention is of wider application, and is not limited to theparticular application described nor to the embodiment illustrated inthe drawing. Reference is therefore to be had to the appended claims fora definition of the limits of the invention.

What is claimed is:

1. In a method of producing light hydrocarbons,

the step of compressing an unsaturated hydrocarbon gas to a pressure ofat least 600 lbs. per square inch, mixing said gas with oil obtained ata subsequent point in the process, heating said mixture to thepolymerization temperature of the unsaturated hydrocarbons while undersaid pressure, separating the mixture resulting from polymerization intoa liquid fraction and a vaporous and gaseous fraction, distilling theliquid fraction to separate the oils from the tars, and returning theseparated oils as the oil mixed with said compressed gas.

2. In a method of producing light hydrocarbons, the steps of compressingan unsaturated hydrocarbon gas to a pressure or at least 600 lbs. persquare inch, mixing said gas with oil obtained at a subsequent point inthe process, heating said mixture to the polymerization temperature ofthe unsaturated hydrocarbons while under said pressure, separating themixture resulting from polymerization into a liquid fraction and avaporous and gaseous fraction, fractlonating said vaporous and gaseousfraction to obtain as separate fractions gas, gasoline and productsheavier than gasoline, distilling the liquid fraction to separate theoils from the tars, and returning both said separated oils and saidheavier than gasoline fraction as the oil mixed with said compressedgas.

' ROBERT M. ISHAM.

